In recent years, in order to achieve high breakdown voltage, low loss, and utilization of semiconductor devices under a high temperature environment, silicon carbide has begun to be adopted as a material for a semiconductor device. Silicon carbide is a wide band gap semiconductor having a band gap larger than that of silicon, which has been conventionally widely used as a material for semiconductor devices. Hence, by adopting silicon carbide as a material for a semiconductor device, the semiconductor device can have a high breakdown voltage, reduced on resistance, and the like. Further, the semiconductor device thus adopting silicon carbide as its material has characteristics less deteriorated even under a high temperature environment than those of a semiconductor device adopting silicon as its material, advantageously.
For example, Japanese Patent Laying-Open No. 2008-147232 (Patent Document 1) describes a trench type MOSFET (Metal Oxide Semiconductor Field Effect Transistor) composed of silicon carbide. According to the MOSFET, in order to prevent punch-through from being caused by a short channel effect, a channel layer is set to have a thickness equal to or more than a length determined by a predetermined formula and a base layer has a lower end located at the drain electrode side relative to the lower end of a gate trench.
Moreover, Y. Nakano et al., “690V, 1.00 mΩcm2 4H—SiC Double-Trench MOSFETs”, Materials Science Forum Vols. 717-720 (2012) page 1069-1072 (Non-Patent Document 1) describes a MOSFET in which a breakdown voltage holding trench is formed adjacent to a switching trench and the bottom portion of the breakdown voltage holding trench is provided at the drain electrode side relative to the bottom portion of the switching trench. A p type base layer is provided below the breakdown voltage holding trench.
Furthermore, according to a trench type MOSFET described in WO 2013/157259 (Patent Document 2), a p type region is provided in contact with the bottom portion of the gate trench.